The present invention relates to an endoscope having a tubular shaft in whose interior is arranged at least one component, in particular lenses, aperture stops, filters, of an optical system, at least one support element that at least partially surrounds the component being provided between the outer side of the component and the inner side of the tubular shaft.
An endoscope of this kind is known from U.S. Pat. No. 4,148,550.
Endoscopes are used generally in surgery to inspect body cavities and hollow organs. Endoscopes have an elongated tubular shaft in which components of an optical observation system are arranged. Further apparatuses, usually a light delivery apparatus, and optionally ducts for instruments, flushing fluid, or the like, are often provided in the interior of the endoscope shaft. Light delivery is usually accomplished via light-guiding optical fibers.
In this case the optical system is received in a separate inner tube in the endoscope shaft.
Endoscopes can be of rigid or flexible configuration, the endoscope shaft correspondingly being manufactured from metal or a flexible plastic material.
The optical systems provided in endoscopes are constructed from components arranged along the tubular shaft axis, such as lenses (in particular rod lenses of the so-called Hopkins optical system), aperture stops, filters, and the like, and their purpose is to reproduce an image of as large a field of view as possible with high resolution and high contrast. The most important prerequisite for this is precise arrangement of the components of the optical system in the tubular shaft of the endoscope. The relative positions of the components of the optical system are not variable but rather are precisely defined, since any shift in the components relative to one another results in decreased image sharpness and resolution.
The components therefore must be precisely immobilized in the tubular shaft of the endoscope so as to remain there immovably.
The components of an optical system are usually slid into the tubular shaft of the endoscope, spaced apart from one another with spacers, and immobilized using end-located terminating elements. This type of immobilization system is insufficient, however, since tolerances can result in radial movement back and forth. A thin air gap is present between the outer side of the components and the inner side of the tubular shaft, or the components rest by way of their outer sides against the inner side of the tubular shaft.
In addition, and most importantly, the lenses of the optical system, made of glass material, can break during handling of the endoscope, for example if the endoscope is dropped or set down too firmly onto a hard surface, since because of the very thin air gap between component and tubular shaft, even slight flexing of the tubular shaft can cause forces or torques to act on the components and result in the breakage of lenses.
This problem has been tackled, for example in the case of rod lenses, by way of a xe2x80x9cdog-bonexe2x80x9d shape for the lens, i.e. a shape in which the ends of the rod lens have enlargements, called rim cylinders. A conforming fit with the tubular shaft is then present only in the region of the rim cylinders, and the remaining periphery of the rod lens is separated from the tubular shaft by a gap.
During cleaning, shocks occur (due to ultrasound, dishwasher, etc.) that cause the lenses to strike against the inner tube as a result of their radial clearance. Impacts also occur between the lens and spacing element (due to wear, contamination, etc.).
One solution to the problem of joining the lenses of an optical system in an endoscope to one another is described in the aforesaid U.S. Pat. No. 4,148,550.
The endoscope described therein has an outer protective tube on whose inner side a layer with light-transmitting fibers is provided, and an inner tube in which a number of rod lenses, which form an optical system, are arranged axially one behind another.
As already mentioned, it is necessary for the operation of the optical system for the rod lenses to be arranged at a defined axial spacing from one another in the inner tube of the endoscope. Spacers in the form of spacer tubes, usually made of metal, are used for this purpose in the existing art.
In U.S. Pat. No. 4,148,550, the join between the rod lenses is created using sleeve-shaped elements which enclose the lens ends of at least two adjacent lenses.
These elements are made of a flexible sleeve-shaped material and have longitudinally extending slots that are provided for the introduction of a tool and the passage of cleaning gases or liquids for the lenses. In addition to holding together the rod lenses that are arranged one behind another, the elements also serve to allow the flexible endoscope to bend while preventing breakage of the rod lenses. These elements themselves can provide bracing with respect to the inner wall of the tubular shaft, but additional annular support elements can also be provided.
Attachment or immobilization of the rod lenses, joined by way of the support elements, in the inner tube of the endoscope is accomplished by press-fitting, specifically by the fact that, for example, a slightly oval or triangular cross section is imparted to the inner, initially cylindrical tube enclosing the rod lens system, so that the rod lenses, with their round cross section, are firmly press-fitted. It is further proposed to use suitable adhesives.
The elements provided in this U.S. Pat. No. document provide for the rod lenses to be joined to one another, and provide for bracing against the parts of the endoscope that surround them. The axially nondisplaceable join must be effected separately, since otherwise the lens arrangement as a whole can move axially back and forth in the interior of the endoscope, which is undesirable due to the adverse effect on optical quality and the risk of breakage of lens elements.
DE 19 12 720 C2 discloses an endoscope whose tubular shaft is made of a transparent and optically clear plastic material into which the optical elements of the objective and the lens system are placed. This hollow cylinder serves as a light guide in order to guide illumination light from the proximal to the distal end of the endoscope.
In order to shield the lenses present in the hollow cylinder from the entry of light from the light guiding system, a light-absorbing and/or reflective element is provided between the hollow cylinder and the objective or the lens system. This element can be configured as a plastic heat-shrink sleeve. The lenses of the lens system and the objective are first placed into this plastic heat-shrink sleeve and positioned in the correct position; then the heat-shrink sleeve is shrunk by the application of heat so that it holds the lenses. This assemblage is then slid into the tubular shaft. The purpose of the plastic heat-shrink sleeve is thus to hold the lenses in a specific orientation with respect to one another, and furthermore to serve as a light-absorbing or light-reflecting element.
DE 33 31 631 C2 has disclosed a lens retaining system for radial adjustment of rod lenses in an optical tube in the region of the lens ends, in which annular retaining means are provided which hold the lenses at a radial distance from the inner surface of the tube.
Against this background, it is the object of the present invention to create an endoscope of the kind cited initially in which the components of the optical system are immobilized as simply as possible but nevertheless securely in the interior of the tubular shaft, and also can be protected against the action of external forces or torques.
This object is achieved, in an endoscope, in that the support element is manufactured from a shrinkable material, and that the component is immobilized on the inner side of the tubular shaft by way of the support element shrunken in the tubular shaft.
A xe2x80x9cshrinkable materialxe2x80x9d for purposes of the present invention is understood to mean on the one hand a cold-stretched thermo-plastic material that contracts back to its original state when heat-treated. The shrinkage effect is based on the effort by the plastic molecules to return to their original, strain-free arrangement. This is also referred to as xe2x80x9cmemoryxe2x80x9d capability or xe2x80x9celastic shape memory.xe2x80x9d Examples of shrinkable materials are PETP, PE, or PVC.
On the other hand, a xe2x80x9cshrinkable materialxe2x80x9d is also understood to mean a metal alloy or a plastic material with a memory effect that has at least two states, one state being achieved via shrinkage of the material. In materials of interest for the invention, the memory effect must be abolished after shrinkage.
This type of immobilization using shrinkable support elements is extremely simple, since the component can first be introduced in accurately fitted fashion into the tubular shaft, along with the support element in its unshrunken, stretched state, and positioned appropriately. As a result of heat treatment, the material shrinks (i.e. contracts) and is pressed into the gap between the outer side of the component and the inner side of the tubular shaft. Depending on the configuration of the support elements, it is possible in this context to use materials that shrink in the direction of the tubular shaft axis and/or that shrink in the transverse direction. What is critical is that the shrinking material fill up the gap between component and tubular shaft in such a way that the component is immobilized, by way of the shrunken support element, on the inner side of the tubular shaft. The heated support element thus adapts both to the external shape of the component and to the internal shape of the tubular shaft, regardless of their individual configurations. After cooling, the shrunken material fills up the air gap between the outer side of the component and inner side of the tubular shaft over certain axial and peripheral regions in the radial direction. Because the material has shrunken into this gap upon shrinking, i.e. attempted to expand radially but was limited because of the narrow gap, the shrunken material exerts an applied pressure that acts radially on both sides and ensures sufficient immobilization of the axial and radial relative position of the component and tubular shaft. Neither adhesives nor other attachment means or clamping connections are necessary, nor do the components need to be fitted exactly into the tubular shaft, since the support element, which is initially stretched and only later is present in shrunken form, ensures immobilization in this case.
The provision of a shrunken support element made of a plastic material has the further considerable advantage that it additionally constitutes protection for the components of the optical system against external forces, since it is elastic and can therefore damp impacts. Even if the endoscope were to be dropped, the risk of breakage of the components of the optical system is thus greatly reduced.
The components of the optical system can, in this context, be lenses, filters, aperture stops, objective cartridges, or any other conceivable components used in endoscope optics. Relevant lenses are rod lenses or conventional lenses; the rod lenses can be provided as smooth cylinders or in a dog-bone, barrel, or any other possible shape. The optical system usually comprises several components arranged axially one behind another, all of which, but optionally also only two adjacent ones of which, can be respectively joined to one another with a shrunken support element according to the present invention and at the same time secured in the tubular shaft.
A xe2x80x9ctubular shaftxe2x80x9d for purposes of the present invention is understood to mean any tubular part of an endoscope in which the optical system is arranged. This will usually be an inner tube that, together with further tubes for the light guide, flushing duct, or the like, is enclosed by an outer tube. If no further ducts are provided in the endoscope interior, however, the tubular shaft can also be the outer shaft of the endoscope. The tubular shaft of an endoscope according to the present does not need to be rigid; it can instead also be flexible, since the shrunken support element is itself flexible and therefore adapts to any bending of the tubular shaft without causing loosening of the immobilization of the component on the inner side of the tubular shaft.
The selection of the material and its shrinkage temperature is also based on the type of endoscope and its intended purpose. Endoscopes in the medical field are sterilized at approximately 140xc2x0 C., so that materials with softening points above 140xc2x0 C. are used. If materials with softening temperatures less than 140xc2x0 C. are to be used, it is possible to provide insulation that ensures, especially with so-called flash autoclaving, that the softening temperature is not reached in the interior of the endoscope shaft. Temperatures of up to 200xc2x0 C. can be tolerated by current optical cements that are used, for example, to close off the tubular shaft at the distal end with an optical window. If materials are used that shrink only at even higher temperatures ( greater than 200xc2x0-400xc2x0 C.), care must be taken that only the shrinkable material is exposed to such high temperatures.
In a preferred embodiment, the support element comprises a sleeve that covers a majority of the outer side of the component.
The provision of a heat-shrink sleeve of this kind offers the advantage of achieving particularly immovable and secure immobilization of the component on the tubular shaft, since the heat-shrink sleeve, so to speak, receives the component within it, i.e. encloses it circumferentially, and thus additionally protects the components from forces on all sides.
It is understood that spacers, for example spacer tubes made of metal or plastic, can also be provided in order to ensure the defined spacings between the components of the optical system, and can then also be immobilized by way of the support element according to the present invention. Spacers of this kind can also, however, be arranged without further immobilization between the components that are immobilized via the support element.
In a further preferred embodiment, the support element comprises at least one ring.
A single ring is advantageously used to immobilize a rod lens present in dog-bone form that is additionally made nontilting in the tubular shaft by way of the rim cylinders provided in the end regions of the rod lenses. The ring is then advantageously arranged in the center region of the dog-bone-shaped rod lens. Annular support elements are moreover particularly be immobilized. The ring then surrounds and immobilizes the entire periphery of such a narrow component.
In a particularly preferred embodiment, the support element comprises two rings that are arranged at opposite ends of the component.
The advantage of this feature is that any tilting of the component inside the tubular shaft is reliably prevented by two support elements that are axially spaced apart from one another. It is also advantageous that annular support elements can be particularly easily slid onto rod lenses when the endoscope is being assembled. It is understood that in particular with elongated components, more than two rings can also be used as support elements.
In a further embodiment, the support element comprises at least one half-ring.
The advantage of this feature is that the immobilization of the component with respect to the tubular shaft according to the present invention can be brought about in a material-saving manner. It is understood that several half-rings, optionally arranged alternatingly on opposite sides of the component, can also be provided.
The fact that a component is not enclosed in completely circumferential fashion by the support element allows the axial passage of gases (e.g. for pressure equalization) or the passage of flushing liquids.
In a further preferred embodiment, the support element comprises at least two strips that extend in the longitudinal direction of the tubular shaft.
Strips of this kind ensure attachment over their entire length, so that even axially elongated components such as rod lenses can be securely immobilized, even if they are not present in a dog-bone shape, while ensuring that tilting within the tubular shaft cannot occur. It is understood that more than two strips can also be provided, the arrangement of three strips being particularly advantageous if they are distributed uniformly around the circumference of the component. A strip of this kind according to the present invention need not, of course, extend over the entire length of the component, but rather can also be substantially shorter, to the point of being xe2x80x9cpadsxe2x80x9d of shrinkable material. Such pads can be distributed in any desired fashion on the outer side of the component.
Pressure equalization of course also occurs when strips are used.
In a further particularly preferred embodiment, the support element comprises a band wound in helical fashion.
A band of this kind wound in helical fashion protects the outer side of the component circumferentially, and additionally provides for the possibility of pressure equalization between the two axial ends of the component. This is because differences in air pressure between the two ends can result in longitudinal forces that can possibly affect the axial position of the components.
In a further preferred embodiment, the outer side of the component is smooth.
The advantage of this feature is that, for example, sleeve-shaped support elements can easily be slid onto the component.
In a further embodiment, the outer side of the component has at least one groove, and the support element is arranged in the region of the groove.
The advantage of this feature is that a particularly intimate join between the outer side of the component and the shrunken material of the support element is achieved. During the heat treatment necessary for shrinking the shrinkable material, the materials shortens while axially increasing in thickness, as already explained. The groove is thereby filled up by the support element. After cooling, the material entering the gap inhibits any axial relative displacement between support element and component.
In a further particularly preferred embodiment, the outer side of the component has at least one land, and the support element is arranged in the region of the land.
The shrunken shrinkage element surrounds the land. It is also possible to provide several lands between which the support element is arranged; in this case the component is additionally supported in the tubular shaft by way of the lands. It is understood that the shape of the land can be rectangular, pointed, or rounded, depending on the conditions of the particular component. The land, projecting into the material and surrounded by it, mechanically inhibits any relative movement between the support element and component.
In a further preferred embodiment, the inner side of the tubular shaft is smooth.
The advantage of this feature is that the assemblage of support element and component can easily be slid into the tubular shaft.
In a further embodiment, the inner side of the tubular shaft has at least one groove, and the support element is arranged in the region of the groove.
When a groove is arranged on the inner side of the tubular shaft, once again the shrinkable plastic material of the support element can expand, during the heat treatment, into the groove, fill it up, and then inhibit any axial relative movement between the tubular shaft and support element.
In an embodiment, the wall of the tubular shaft has at least one outwardly directed protrusion in the form of a spherical segment, and the support element is arranged in the region of the protrusion.
This feature offers the considerable advantage of protecting the component especially well from outside forces, since a particularly thick bead-like layer of the damping material is present between the component and the tubular shaft wall precisely in the region of the contact surface with the tubular wall, specifically above one or more protrusions.
In a further embodiment, the inner side of the tubular shaft has at least one land, and the support element is arranged in the region of the land.
In this case the land is surrounded by the support element and inhibits any axial displacement of the support element relative to the inner side of the tubular shaft.
In a preferred embodiment, several components are arranged axially in the interior of the tubular shaft along the tubular shaft axis; and the support element extends over the components and the latter are thus immobilized in an axial arrangement with respect to one another.
The considerable advantage of this embodiment is not only that the support element guarantees immobilization of the components on the inner side of the tubular shaft, but also that the individual components of the optical system, arranged axially one behind another, are also immobilized relative to one another. Thus not only it is possible to prevent any axial displacement of the individual components in the tubular shaft, but the spacing between the individual components that is necessary for correct functioning of the optical system is additionally fixed and ensured. The support element according to the present invention thus performs three functions: firstly, the components are immobilized on the inner side of the tubular shaft; secondly, the components are joined to one another and immobilized with respect to one another; and thirdly, the components are protected over their entire length from external forces, since the latter are damped by the elastic material. Any movement of the components of the optical system in the tubular shaft that might adversely affect the optical system is thus practically ruled out.
The object of the invention is furthermore achieved by a method for mounting components, in particular lenses, aperture stops, filters, of an optical system, in the interior of a tubular shaft of an endoscope, in which at least one support element that at least partially surrounds the component is brought onto the outer side of the component of the tubular shaft, and this assemblage is introduced into the tubular shaft, that is characterized in that a support element made of a shrinkable material is applied; and after introduction of the assemblage into the tubular shaft, a heat treatment is performed such that the material of the support element shrinks, thereby immobilizing the assemblage on the inner side of the tubular shaft.
This method for mounting components is particularly simple, since the support element is first brought, in its stretched initial state, onto the component outside the tubular shaft, or the components are slid into it; and only then is the assemblage introduced into the tubular shaft, sufficient radial clearance being present to easily allow such installation, since in this state the shrinkable material is only a thin film. It is only as a result of the heat treatment that is then performed that the shrinkable material increases in thickness, and creates the intimate contact between the inner side of the tubular shaft and the outer side of the component. If grooves, lands, elevations, or other elements are provided on one of the participating surfaces, these are, so to speak, xe2x80x9csurroundedxe2x80x9d and xe2x80x9cfilled upxe2x80x9d by the shrinkable material that is in a rubber-like state as a result of the heat treatment.
In a preferred development of the method according to the present invention, several components are arranged axially one behind another along the tubular shaft axis, and a support element extending over the several components is applied in such a way that after the heat treatment, the components are additionally immobilized relative to one another in their axial arrangement.
The advantage of this feature is to guarantee, without additional actions, that the components are immobilized in the interior of the tubular shaft and are joined and immobilized relative to one another. The components can be lined up outside the tubular shaft and then joined together by way of the support element; this is particularly easy because visibility is not blocked by the tubular shaft. Only then is the assemblage slid into the tubular shaft.
The heat treatment and the material properties of the shrinkable material ensure that the components are arranged inside the tubular shaft in a manner protected against axial and radial displacements. Two kinds of immobilization of the components are thus achieved, namely immobilization on the tubular shaft and immobilization relative to one another.
It is understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the context of the present invention.